Perhaps you can clarify a few things , if you kept your previous supplier running , presumably this is not on the Openreach network, so who is it , and is it this supplier providing the phone number you want to port to BT ?.
If you now have a BT service , is that with a phone service and is that phone service DV ( so via your BT broadband router ? )
This statement needs clarification, Once ported it will cancel my broadband as it's a digital voice number (out of the back of the ont), this is fine as I wanted to switch services to bt anyway, I'm not currently a bt digi voice landline and want to keep it that,
DV is BT’s proprietary phone offer , it’s not a generic term for every providers IP telephony, if you use DV when referring to other companies IP telephony it will cause confusion.
If whatever Alt Net you currently use are suppling you with some sort of an IP phone service and you want to keep that number by porting it to BT , because you already have ‘BT’ with either no phone number or a BT supplied number , you cannot port the number from the Alt Net to this working BT ‘line’ ( well not directly )
You could order a second BT service , and at sign up ask for the Alt Net phone number to be ported to your new second line , or cease your current existing BT service ( expensive for ETC if you are within a minimum term ) and then reorder and again at order entry ask for the Alt Net number to be ported , or simply export the Alt Net number to a regular VoIP provider , and use your BT broadband to access it , but that wouldn’t be via the phone port on the BT SH2 , but using whatever method this third party VoIP provider requires.
What you will probably find is that you cannot renumber you existing BT service with the number from your current Alt Net provider with a single transaction.
